Method and apparatus for machining work pieces

ABSTRACT

A method and apparatus are provided to machine a curved surface such as an inner or outer peripheral surface of a pipe. The pipe is held stationary during machining and a rotatable spindle of a machine head moves along multiple orthogonal axes to align the rotational axis of the spindle with the longitudinal pipe axis. Preferably, the pipe axis is located by using a touch probe to engage the curved surface at multiple spots and the calculating the location of the pipe axis. The cutting tool, which is preferably a cutting tool insert, is rotated by the spindle to machine the curved surface.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of prior Application Number11/774,049, filed Jul. 6, 2007, now U.S. Pat. No. 7,674,079 B2, issuedMar. 9, 2010, which claims benefit of U.S. Provisional Application No.60/806,673, filed Jul. 6, 2006, which are both hereby incorporatedherein by reference in their entirety.

FIELD

The invention relates to a machining system and a method of use thereof,which is particularly useful for machining large size, work pieces, suchas large pipes.

BACKGROUND

Pipe used in the oil and gas industry can be about 2 feet in diameterand up to about 30 feet in length. These pipes typically have threadingcut on an inner or outer diameter of each end for use in connectingadjacent sections of pipe together. Such large pipes, however, presentchallenges in cutting the threads in an efficient, safe, and costeffective manner. Current equipment for machining pipe threads on theselarge pipes is either a commercially available lathe or a horizontalmachining center. However, each machine has constraints that render themachining of large size work pieces, such as pipeline for the oil andgas industry, difficult and time consuming.

One approach of threading large size pipe is to use the commerciallyavailable lathe. This equipment rotates the pipe along a horizontal axisthereof, and a stationary tool cuts the thread on the end of the pipe asit is rotated. In order to secure the pipe to the lathe, the one end ofthe pipe that is rotated is passed through the center of the latheheadstock and is secured thereto by clamping using chucks with grippingjaws located on the front and rear of the headstock. In order for thelathe to function correctly, the pipe must be centered on the lathehorizontal turning axis. The centering of the pipe along the lathe axisis a time consuming, labor intensive task that must be completed eachtime a new pipe is installed into the lathe. The centering operation iseven more difficult with the large size pipes used in the oil and gasindustry.

In order to center pipe on the lathe, current methods use a fixedindicator placed in the end of the pipe at the headstock. The pipe isthen slowly rotated by hand in the chuck until the inner surface of thepipe contacts the indicator. When the indicator signals that the pipe isnot rotating on the center of the lathe axis, the chuck jaws must thenbe loosened and the pipe readjusted. This trial and error process isthen repeated until the pipe rotates on the center of the lathe axis assignaled by the indicator. This centering process is an extremely timeconsuming task that must be performed each time before the machining canbegin on a new pipe. Only one end of the pipe is threaded so that tothread the other end of the pipe, it must be turned through 180 degreesto position the pipe end previously in the support area at the chuck.

Even after the large diameter pipe has been centered so that properlathe cutting can be performed, rotating such large size pipe (i.e.,about 30 feet long and about 2 feet in diameter) can also create safetyconcerns as well. For instance, sufficient guarding must be providedaround the lathe and work piece in order to protect the operators andsurrounding areas from the rotating part during machining. In addition,many pipes may be unbalanced, which creates technical and other safetyissues when rotating. Rotating an unbalanced pipe at high speeds can putstress on the headstock bearings causing premature failure. Theunbalanced pipe can also cause accuracy issues by causing anout-of-round condition on the threading machining. In response tounbalanced work pieces, operators need to slow the rotational speed ofthe pipe in the headstock in order to minimize any effect of theout-of-round condition. A large pipe also has considerable inertia to beovercome to start and stop of its rotation. Slower lathe speeds resultin less than optimal cutting conditions, and also reduce tool life andadd cycle time to the overall process.

Another conventional method of threading pipe is to use the horizontalmachining center. In this method, the pipe is secured to a table so asnot to rotate, and then moved horizontally relative to the cutting tool.The horizontal machining center provides advantages over the lathesystem because the pipe does not rotate. However, current horizontalmachine centers also have shortcomings such as size of the movableworktables when machining large size work pieces, such as the 30 footlong pipe for the oil and gas industry.

In a typical horizontal machining center, the machine table is an axisthat must be able to move longitudinally as part of the machiningoperation. That is, the table must move horizontally along a feed axisso as to feed the part into the cutting head. Current movable tables arerestricted in size, and only limited sizes of pipe can be mountedthereon. Existing tables are configured to accept part lengths up toabout 10 feet. Constructing larger moveable tables, such as tablescapable of handing a 30 foot long pipe, is not a cost effectivesolution.

In addition to physical constraints with the size of work piece suitablefor cutting on the horizontal machining center, the thread cut by thehorizontal machining center is less preferred. The threading of theinner or outer diameter of the pipe on current horizontal machiningcenters is through a circular interpolation movement of the tool aboutthe non-rotating pipe rather than a true circular movement as obtainedwith the lathe. The circular interpolation is created by moving themachine head along two linear axes in small step movements around thecircumference of the pipe to position the cutting tool at the depth orin-feed for cutting the thread. Since the thread is generated using acombination of these small linear steps, the quality of the thread andaccuracy is not as good as a thread generated on a rotational axis suchas used on a lathe.

When cutting a thread on piping, the horizontal machining center alsotends to be more expensive to operate. For example, because of thecircular interpolation movement, the cycle or cutting time is muchlonger compared to turning the thread on a lathe because the metalremoval rate is less with thread milling (i.e., horizontal machiningcenter) than with turning on a lathe. The perishable thread mill toolused on the machining center is also more expensive than indexableinserts used on threading tool holders in a lathe. The thread mill toolsare specially ground to the thread form that they are needed to generateand must be reground when worn or discarded completely if broken. Theindexable inserts commonly used in lathe operations, on the other hand,are readily available in the industry for many types of thread forms andeasily changed when they are worn or broken.

The drawbacks of circular interpolation may be overcome by the use of arotary spindle head configured to rotate a cutting tool about arotational axis to cut a circular thread. An example of such a head isthe U-TRONIC head available from D'Andrea, S.P.A. The cutting tool ispositioned radially along a feed-out axis to engage the work piece atthe proper thread depth and then rotated to cut the thread. However, insuch systems the pipe is translated along its longitudinal axis duringmachining, creating the drawbacks discussed above associated with movingthe machine table during the machining operation.

The horizontal machine centering also suffers from similar trial anderror shortcomings described above in connection with the lathe whencentering of the work piece. Current methods require a similar indicatorthat is mounted to the headstock center line that is swept around theinner diameter of the pipe by hand. If the indicator signals that thepipe is not on-center with the headstock then the pipe must be adjusted.As with the lathe, this process is repeated until a sweep of theindicator signals that the pipe inner walls are on the center of themachine axis. This manual process is time consuming and tedious and alsomust be completed each time a new pipe is to be cut.

Therefore, there is a desire for a machining system and a method of usetherefore, that overcomes many of the disadvantages of these prior artlathe and horizontal machining centers heretofore used with large sizework pieces, such as 30 foot long pipe designed for the oil and gasindustry.

SUMMARY

A new and improved method and apparatus are provided for machiningcurved surfaces such as outer and/or inner peripheral surfaces of apipe. This new method and apparatus will be described in connection withan illustrated embodiment used to machine large pipes; however, themethod and apparatus is not limited to only such uses. In theillustrated embodiment, the curved surfaces are cylindrical surfaces onthe ends of very large pipes and threads are machined on opposite endsof the pipe. In the preferred system, the pipe is stationary. It isneither fed along a head axis relative to the cutting tool nor rotatedduring the cutting operation. This avoids inertia, balancing and safetyproblems encountered in rotating large, heavy pipes in prior art lathesand other disadvantages encountered when using horizontal machinecenters as discussed above.

In accordance with an aspect of the apparatus, the pipe is mounted on astationary work support and is not translated or rotated relative to thecutting tool. Instead, the cutting tool is translated along a radialfeed-out axis to engage the work piece and then the spindle carrying thetool is rotated to machine the surface while the spindle and tool areadvanced along an in-feed direction, which is parallel to thelongitudinal pipe axis when a pipe is being machined. When thismachining is completed, the tool is retracted from work pieceengagement. Thus, only the tool is moved during thread cutting.

For machining long, large pipes, the machine tool or head is positionedto face one end of the pipe with at least a three axis machine toolhaving a headstock and a spindle which in-feeds in a direction parallelto the longitudinal axis of the pipe. The cutting tool is advanced alonga feed-out axis to a particular depth position for cutting the pipe'sinterior side wall and/or its exterior side wall at the facing end ofthe pipe.

To achieve increased efficiency, a machining tool may be located at eachof the pipe ends, and both ends of the pipe may be machinedsimultaneously because the pipe itself is held substantially stationary.This substantially improves the machining capacity and efficiency ascompared to machining one end at a time in the prior art commercial pipethreading machines.

In accordance with another aspect, the center axis of the pipe islocated in an automatic manner using a touch probe or the like mountedon the machine tool without manual intervention in a trial and errorprocess as is conventionally done. Preferably, the center axis of thepipe is determined using calculations and the tool machine zero point ofthe coordinate system is adjusted to match the work piece axis. The toolhead and spindle are then shifted to this pipe center axis and then thetool is shifted along the feed-out axis relative to the spindle to theproper depth or cutting position.

In accordance with another aspect, the cutting tool uses an indexabletool insert as the cutting tool to machine a thread on the work piecerather than expensive custom thread mills to generate the thread. Also,the cycle or cutting time is less using the present invention ratherthan an expensive thread, milling machine process to generate thethread.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an exemplary machining center withmultiple work pieces being shuttled into and out of an operativeposition in the machining center;

FIG. 2 is a perspective view of a headstock used with the machiningcenter illustrated in FIG. 1;

FIG. 3 is perspective view of a multi-axis head of the machining centerof FIG. 1 showing multiple axes of movement thereof;

FIG. 4 is a perspective view of the headstock of FIG. 2 showing a rotaryspindle and an exemplary indexable insert cutting tool thereon;

FIG. 5 is another perspective view of the multi-axis head of FIG. 3showing a tool loading mechanism;

FIG. 6 is an alternative view of the rotary spindle with an exemplarythread mill tool thereon;

FIG. 7 is a schematic view showing the relative relationship between amachine coordinate system and a work piece coordinate system;

FIGS. 8A and 8B are schematic views showing a procedure forautomatically centering the machining center of FIG. 1 to the actualcenter of the work piece;

FIGS. 9A and 9B are schematic views showing a procedure for using a failsafe stop mode using both relatively slow and fast strokes of thecentering probe during the automatically centering procedure to preventdamage to the centering probe;

FIG. 10 is a flow chart showing an exemplary method to determine the anactual work piece center;

FIG. 11 is a schematic view showing an exemplary method of using themachining center of FIG. 1 to automatically measure and calculate theactual work piece center and to machine the work piece;

FIG. 12 is a flow chart showing an exemplary method of using themachining center of FIG. 1; and

FIG. 13 is a perspective view of an alternative material flow layoutusing four machining centers so that both ends of two work pieces can bemachined at the same time.

DETAILED DESCRIPTION

Referring to FIGS. 1-6, a system for machining large size work pieces inthe form of a machining center 10 is illustrated. The machining center10 employs a work piece 12 and a cutting tool 14 that is rotatablymounted to a machining head 16. Preferably, the machine center 10 isconfigured to machine large work pieces 12, such as pipeline for the oiland gas industry. Such pipes may have a diameter of about two feet and alength of about thirty feet; however, the center 10 may be used tomachine work pieces 12 of larger or smaller dimensions.

In accordance with the illustrated embodiment, the work piece 12 isfixed, that is, the work piece 12 does not rotate or translate along afeed axis into the cutting tool 14. The machine positionings relative tothe work piece are accomplished by movement of the cutting tool andmachining head relative to the fixed work piece. In this illustratedembodiment, the opposite ends of the pipe are machined simultaneously intwo cutting operations—one on each end of the work piece 12—to doublethe efficiency over the prior art systems, which can only machine oneend of the work piece at a time. In the prior art lathes, only one endof the work piece can be cut at a time because the other end is beinggripped to rotate the pipe. In the prior art horizontal machiningcenter, the work piece is fed horizontally into the cutting head;therefore, a second tool cannot operate on the opposite end of the workpiece because the work piece would actually be moving away from anysecond cutting head.

Referring to FIGS. 1 and 2, the machine center 10 includes at least oneand preferably two multi-axis machine tools 18, and at least one andpreferably a plurality of fixtures or work supports 19 onto which eachof the work pieces 12 is clamped. The multi-axis machining head 18includes the cutting tool 14 mounted in a rotary spindle 15 coupled tothe machining head 16. The head is operative to translate in each ofthree horizontal, vertical, and rotary axes. Herein, each of the worksupports 19 shuttles the work pieces 12 fixed thereon into and out of anoperative position at a machining position in the machining center 10.During machining, however, the work support is fixed on a stationarymachine bed 26 of the machining center. That is, the work support 19 ismoveable from a loading position L, where the work piece 12 is clampedthereon prior to machining, to an operative position O, where the workpiece is fixed during machining operations. During machining, allmovements occur in the multi-axis machining head 18 without having tomove either the work piece 12 or the work support 19. In other words,during the cutting or threading operations, the work piece 12 and worksupport 19 are stationary and not rotated or fed into the cutting tool14.

By not moving the work piece 12 during machining, many of the problemswith the prior lathe systems have been eliminated. For example, theinertia, balancing and safety concerns of rotating or moving largediameter or long parts has been eliminated providing a safer machiningcenter. There is no longer any need to feed the work piece through theheadstock of the machine, which often constrained the size of theheadstock and/or machine. Moreover, by not rotating the work piece 12,there is less stress on bearings and other components, which isespecially beneficial when machining parts that may be out of balance.Eliminating the need to rotate of out-of-balance parts should alsoprovide a better quality thread by eliminating the part out-of-roundnesscaused by an unbalanced condition during rotation.

The machining center 10 is also an improvement over prior art systemsbecause the work piece 12 can be fixed very quickly and inexpensively tothe work support or fixture 19 off-line in the loading position L andthen automatically shuttled to the operative position O within themachining center 10. The work piece can also be secured to the worksupport 19 using inexpensive strap clamps rather than large expensivethrough hole chucks in which the work piece 12 would need to be able topass through. In this regard, there is also little concern of centeringthe work piece 12 onto the work support 19 or even centering the workpiece and mounting device assembly into the machining center 10. Thus,operator set-up time is significantly reduced and there is no need toemploy precision locators in order to center the work piece. Moreover,as further described more below, the centering operation may becompleted automatically using the multi-axis machine tool 18—minimizingthe need for manual, operator intervention. For example, a centeringprobe 22 (FIGS. 8A, 9B, and 11) may be employed along with themulti-axis head 18 to determine the actual center axis of the work piecerelative to a machine coordinate system without needing to move orreadjust the fixed work piece 12. Once the actual work piece center axisis identified, then a machine coordinate system 54 (i.e., machine zeropoint) (FIG. 7) can be automatically adjusted in order to match the workpiece actual center axis. This avoids the time consuming trial and errorprocedures of a lathe where the pipe is repositioned until its axis isproperly aligned for the threading operation and of a milling machinecenter where the spindle axis is readjusted through a trial and erroruntil the spindle axis is aligned with the longitudinal axis of the workpiece. The use of mathematical calculations to readjust the machineorigin eliminates the need to move the pipe or the spindle axis usingthe prior art slow trial and error procedure when machining pipe ends.

The center 10 also preferably machines the work piece 12 in an automaticoperation. After automatic centering, the appropriate cutting orthreading tool 14 having the proper thread form is automatically loadedinto the rotary spindle 15 of the machine head 16. The head 16 includesboth a rotational axis as well as a feed-out direction or axis. As willbe discussed further below, the cutting tool 14 will be fed out usingthe feed-out axis X1 to the proper cutting diameter and then rotatedusing the rotational axis “C” of the headstock 16. The tool 14 will thenbe moved into the work piece 12 along the Z axis (rather than moving thework piece) in order to cut the thread. A feed-out head 24 (FIGS. 2 and4) will extend the tool 14 along the X1 axis for each cutting pass untilthe proper thread depth is reached. This method of machining shouldprovide at least the same quality thread as prior lathe turningoperations since it generates the thread using a rotational axis. Themethod can provide a superior thread compared to the circularinterpolation method of the prior thread milling methods used on ahorizontal machining center. It also overcomes the shortcomingsassociated with prior systems utilizing a rotary head in combination ofa linearly advancing work table.

The machining center 10, therefore, also permits the use of inexpensive,readily available indexable inserts 21 commonly used in lathe systemrather than the more expensive custom thread mills used with traditionalhorizontal machining centers. Since the machining center 10 does not usethe thread milling process of circular interpolations for repositioningthe cutting tool to generate the thread, the cycle time or cutting timewould also be much less comparable to the lathe turning process.

Turning to more of the details, the work piece 12 may be fixed tomounting or work support 19 in various manners. In one example asillustrated in FIG. 1, the work support 19 includes a base 19 a and twospaced support arms 19 b on opposite ends of the base 19 a. As the workpiece 12 is preferably a pipe, each support arm 19 b preferably includesa saddle surface 19 c to support the work piece 12 therein. That is, thesurface 19 c preferably has a curvature to match the curvature of thepipe. Clamps 19 d, such as inexpensive strap clamps, chucks, and thelike, then secure the pipe to the table arms 19 b. The work piece 12 isloaded onto the work support 19 so that the area to be threaded isfacing the headstock 16 when the work piece 12 is moved to the operativeposition O in the machine 10. It should be noted that the work support19 illustrated in FIG. 1 is exemplary and other suitable mountingdevices, work tables or fixtures may also be employed for supporting thework.

The work support 19 is operative to translate along the machining centerbase or floor 26 from the loading position L to the operative positionO. In this manner, the work piece 12 may be fixed to the work support 19as described above “off-line” and then fed into and out of the machiningcenter 10 in an automated manner. Preferably, each of the succession ofwork supports 19 moves along the machine base 26 via a movement device28, such as a track, rail, slide, wheel, bearing, conveyor, or othersuitable movement fixture from a loading position and then move into thethreading cutting position, and after the thread cutting operation to anunloading position.

Referring more specifically to FIGS. 2-5, the multi-axis machining tool18 is operative to move the cutting tool 14 about a variety of axes.That is, the machine tool 18 is configured to position the cutting tool14 in the proper cutting location through movement of the tool along avariety of horizontal, vertical, and rotational axes. In order to movethe cutting tool 14 in such manner, the machine tool 18 includesmultiple components, each of which are configured to move along adifferent axis.

For example, as best shown in FIGS. 3 and 4, the illustrated machinetool 18 includes a movable base slide or saddle 30 configured totranslate along a horizontal slide 35 along an axis Z relative to thebase 26. The axis Z is generally parallel to the work piece axis and isused to feed the cutting tool 14 into and out from the work piece 12. Inone embodiment, the movable base 30 has a stroke or operative distanceof about 65 inches along the Z axis. On the saddle 30, a support column32 is disposed on an upper surface 31 of the saddle 30. The column 32 isoperative to move relative to the saddle 30 along a horizontal axis X2,which is normal to the Z axis and to this end is mounted on slides 37between the bottom of the column 32 and the top of base 30. As thecolumn moves along the X2 axis, the cutting tool 14 is movedhorizontally relative to the base 26 and transverse to the Z axis. Inone embodiment, the column 32 has a stroke or operative distance ofabout 30 inches along the X2 axis of the movable base 30. The machinehead 16 is mounted to a side wall 33 of the column 32 and is configuredto translate up or down the length of the column 32 along a verticalaxis Y, which is transverse to both the Z and X2 axes. Vertical slidesor ways 39 on the column 32 guide the machine head 16 for travel alongthe Y axis which results in the cutting tool 14 traveling verticallyrelative to the base 26. In one embodiment, the machine head 16 has astroke or operative distance of about 26 inches along the Y axis of thecolumn 32. Mounted to the machine head 16 is the rotary spindle 15,which rotates relative to the machine head 16 along a rotary axis C. Inone form, the rotary spindle 15 is configured to rotate between about200 to about 500 rpm. Within the rotary spindle 15 is a small feed-outhead 24 that translates inwardly or outwardly relative to the rotationalaxis C of the rotary spindle 15 along the feed-out axis X1, and the toolis shifted along this X1 axis to engage the cutting tool 14 with thework piece and also to achieve the proper thread depth being cut. In oneembodiment, the feed-out head 24 has a stroke or operative distance ofabout 12 inches along the X1 axis relative to the rotary spindle 15 andprovides about 8 inches of extension from the rotary spindle. In thismanner, the machine tool 18 provides for large horizontal adjustmentalong the X2 axis and fine horizontal adjustments along the X1 axis.While exemplary dimensions are provided above, which are preferred tomachine a pipe 12 having a diameter of about 22 inches, it will beappreciated that larger or smaller dimensions are also acceptable tomachine larger or smaller work pieces.

Turning to more of the details, as best seen in FIG. 4, the feed-outhead 24 comprises a feed-out slide 24 a mounted for sliding acrosscircular end wall 15 a of the spindle 15 within a pair of slides orgrooves 15 b. Herein the feed-out slide 24 a comprises a flat plate orbase 24 b on which is fixed, in a cantilevered manner, an inner end of acylindrical shaft 24 c on the outer end of which is mounted the cuttingtool insert 21. The feed-out slide 24 a is spaced outwardly along theend wall of the spindle relative to the center of the spindle axis C.The feed-out head 24 may be obtained, for example, from D'Andrea,S.P.A., Italy, but other suitable heads may also be used.

The center 10 machines the fixed work piece 12 through combinations ofmovements along the above described axes. Preferably, each abovedescribed component may move along its associated axes via slides orother devices, such as a track, rail, slide, way, bearing, wheel,conveyor, spindle, or other suitable movement fixtures. Movement alongeach of the respective axes is may be controlled through conventionalstepper motors or other conventional precision movement control devices.

Referring to FIG. 5, the multi-axis machining head 18 also preferablyincludes a tool loading mechanism 40 to automatically load one of avariety of different tools 42, such as one or more cutting tools 14 orthe centering probe 22. The loading mechanism 40 includes a toolmagazine 44, which stores the tools 42 thereon when not in use, and anautomatic tool change arm 45 that selects and moves the desired tool 42from the magazine 44 to the machine head 16. In one form, the toolmagazine is a disk configured to rotate in order to position a desiredtool 42 in a tool receiving position 46 where the arm 45 may select andgrab the desired tool. In one embodiment, the tool magazine 44 mayinclude 24 tools, but more or less tools may be included as needed.

Referring to FIG. 6, the rotary spindle 15 of the machine head 16 isshown using an alternative cutting tool 114, which is in the form of anexemplary thread mill tool. In this form, the tool 114 is configured tomachine multiple threads using a circular interpolation method. In thisalternative approach, for example, the thread mill tool 114 rotates asshown in the figure.

To properly cut either inner or outer diameter threads on a work piece12, such as a pipe 12 a, the actual center of the pipe 12 a is firstdetermined. Referring to FIGS. 7-10, an exemplary automatic centeringprocedure is illustrated that may be used with the machining center 10in cooperation with the centering probe 22 and the multi-axis head 18.As shown in FIG. 7, the automatic centering procedure generally comparesa machine coordinate system 54 to a work piece coordinate system 52 tocorrectly position the headstock 16 at an actual work piece center 50after measuring the dimensions of the work piece. In general, thecentering probe 22 is first mounted to the headstock 16, and then themulti-axis head 18 moves the probe 22 along a predetermined path tomeasure the pipe 12 a dimensions in order to calculate an actual pipecenter 50 relative to a work piece coordinate system 52. Then, a machinezero point 60 within the machine coordinate system 54 is adjusted, ifneeded, to match the work piece coordinate system 52 based on an offsetdistance from the actual pipe center 50 and a projected pipe center 58.

By one approach, the centering probe 22 is preferably a coordinatemeasuring probe such as a touch sensor probe (Renishaw, PLC, UnitedKingdom) having a stylus on a measuring end that measures the dimensionsof the work piece pipe after being automatically mounted into themachine spindle 15 on the machine head 16. The centering probe 22 ispreferably stored in the tool magazine 44 and transferred to the rotaryspindle 15 of the headstock 16 through the automatic tool change arm 45when a new work piece 12 is loaded into the operative position. Onceautomatically mounted in the headstock 16, the centering probe 22preferably locates the actual center 50 of the work piece 12 bycontacting multiple interior positions through movements of themulti-axis head 18. From these positions, the actual center 50 andoffset distance from the projected center may be determined. Asdescribed below, the probe 22 preferably contacts at least fourpositions on the pipe 12 a inner surface, but any number of contactpoints may be used at various positions on the work piece 12 in order todetermine the geometry and dimensions thereof. Alternatively, the probe22 may contact a plurality of positions on an outer surface of the pipe12 a.

Referring to FIGS. 8 to 10, an exemplary centering procedure 100 isillustrated in more detail. Once the centering probe 22 is automaticallymounted in the headstock 16, the multi-axis machine tool 18 will movethe probe 22 along the exemplary machine paths 51 and 53 to position theprobe 22 within the interior of the pipe 12 a oriented 102 along theprojected center axis 58. At this point, the machine tool 18 will shiftor translate 104 along a predetermined path to measure the innerdiameter of the pipe along both an Xw axis and an Yw axis (which aregenerally orthogonal to each other) of the work piece coordinate system52 so that an offset distance β of the actual center axis 50 from aprojected center axis 58 can be calculated. Preferably, the offsetdistance β includes distances along each of the orthogonal axes Xw andYw and, therefore, has an X component and a Y component (βx and βy). Theprojected center 58 is based on the nominal diameter D of the pipe 12 a.

More specifically, the multi-axis machine tool 18 will first move theprobe 22 to the projected work piece center 58. The multi-axis machinetool 18 will then move the probe 22 vertically upwardly along the workpiece axis Xw (Arrow A) until the probe stylus contacts an upper point62 of an inner surface 63 of the pipe 12 a. The probe 22 will then bemoved vertically downwardly along the same axis Xw (Arrow B) until thestylus of the probe 22 contacts a lower point 64 of the inner surface 63of the pipe 12 a. In this manner, the predetermined path of the probe 22generally forms a chord of the pipe 12 a. The distance between the upperpoint 62 and the lower point 64 along the Xw axis is calculated 106 anddivided in half 108 to determine the midpoint Xm along the Xw axis. Anoffset distance βx along the axis Xw between the projected center 58 andthe actual center 50 is calculated 110 based on the distance from theprojected center to the Xw axis midpoint Xm. As discussed below, asimilar procedure is used along the Yw axis.

Next, the multi-axis machine tool 18 will re-position 102 the probe 22to the projected center 58 (Arrow C) and move 104 the probe horizontallyin a leftward direction along the axis Yw (Arrow D) until the probestylus contacts a left point 70 on the inner surface 63 of the pipe 12a. The probe 22 will then be moved in a rightward direction along thesame axis Yw (Arrow E) until the probe stylus contacts a right point 72on the inner surface 63 of the pipe 12 a. The distance between the rightpoint 70 and the left point 72 is calculated 106 and divided 108 in halfto determine the midpoint Ym of the pipe along the Yw axis. An offset βyalong the axis Yw between the projected center 58 and the actual center50 is calculated 110 based on the distance from the projected center tothe Yw axis midpoint Ym. The probe is then retracted out of the workpiece 12 generally along machine paths 51 and 53.

The distance from the projected center 58 along the Xw and Yw axes tothe actual center 50 is the calculated offset distance (βx, βy). Thezero point 60 of the machine coordinate system 54 is then adjusted bythe same offset (βx, βy) to an adjusted machine zero point 61 in orderto match the machine coordinate system 54 to the actual work piececenter 50 (FIG. 8B and FIG. 9A). This centering procedure is completedwith minimal, and preferably no, manual intervention by the operators,such as re-adjusting the work piece, in contrast to procedures for theconventional lathe and milling machines for machining large pipes.

Referring to FIGS. 9A and 9B, the automatic centering method may alsoemploy a fail safe stop mode in case the nominal inside diameter Di ofthe pipe 12 a is significantly different that what is being measured bythe probe 22. The nominal diameter Di may be different than what isbeing measured because it was incorrectly inputted into the controlleror the nominal diameter was incorrectly provided with the new pipe. Thisfail safe stop mode prevents damage to the centering probe 22 or thestylus thereon due to an incorrect pipe diameter.

For example, during a measurement cycle, when the probe 22 approaches apredetermined distance to the inner wall 63, the multi-axis machine tool18 will move the probe 22 slower until it actually contacts the wall 63.Preferably, once the probe 22 is within the predetermined distance tothe pipe inner wall 63, such as a distance K, the probe 22 will moveslower until it either contacts the pipe inner surface 63 or does notcontact the pipe within a predetermined length of movement (i.e., a timeout distance). The distance K may be determined as a percentage of thenominal inside diameter Di of the pipe. By one approach, the distance Kis about 10 percent of the inside diameter Di; however, other distanceswill also work. If the probe 22 does not contact the wall 63 within thisset limit K, then an error message or alarm will be signaled to indicatethat the work piece 12 a has a size different than originally expected.

For example, as best illustrated in FIG. 9, the probe 22 initially movesrelatively fast along the Yw axis, such as along Arrow F until itreaches the distance K from the pipe wall 63. At this point, the probe22 moves in a relatively slow speed represented by the wavy Arrow Gthrough this distance K until the probe actually contacts the wall 63 orfails to contact the wall within the prescribed distance. The probe 22will preferably operate in a similar manner when moving along the otheraxes.

A similar centering procedure may also be used to determine thethickness and/or outer diameter (Do) of the work piece 12. For example,the probe 22 may contact opposing outer surfaces 65 of the work piece 12in a similar manner to that previously described except that the probe22 will be outside the work piece 12 rather than measuring inside thework piece 12. For example, the probe 22 may be positioned to contactopposing points 67 and 69 on the outer surface 65 of the work piece 12generally along the Xw axis, and also contact opposing points 71 and 73on the outer surface 65 of the work piece 12 generally along the Ywaxis. Then, differences between the inner contact points (62, 64); (70,72) and the outer contact points (67, 69); (71, 73), respectively, maythen be used to calculate a thickness of the work piece.

Referring to FIGS. 11 and 12, an exemplary method of machining the workpiece 12 using the machining center 10 is generally illustrated. In thisexample, the work piece 12 is preferably the pipe 12 a; however, themethods described herein may also be used in a similar fashion tomachine other types of work pieces.

First, the pipe 12 a is mounted 1002 into the fixture or work support19. Second, the pipe 12 a is clamped 1004 to the work support 19 usingthe clamps 19 d, such as the inexpensive strap clamps. As discussedabove, the mounting and clamping steps can be completed off-line in theloading position L (FIG. 1). When the machining center 10 is ready tomachine the pipe 12 a, it is shuttled into the operative machiningposition O (FIG. 1). (The remaining steps illustrated in FIG. 11 showthe mounting device and clamp 19 d removed for clarity.) Third, thecentering probe 22 is automatically selected 1006 by the automatic toolchange arm 45 and mounted to the rotary spindle 15 of the machine head.The centering probe 22 then is used to determine 1008 the actual pipecenter 50 and calculates 1010 the actual center 50 of the work piece andcalculates 1012 an offset β from the projected work piece center 58. Theoffset β is used to adjust 1014 the machine zero point 60 within themachine coordinate system 54 an amount corresponding to the offset β sothat the machine coordinate system 54 is matched to the actual center 50of the pipe 12 a. As mentioned above, this centering process is competedwithout the time-consuming repositioning of the work piece 12 or thework support. Fourth, the desired cutting tool 14 is selected andinterchanged 1016 with the probe 22 by the automatic tool change arm 45.Fifth, the saddle 30, column 32, headstock 16, and feed-out head 24shift the tool 14 near the exterior or interior surface of the pipe endthrough various combinations of movement along the X1, X2, Y, and Zaxes. The rotary spindle 15 is then rotated at a predetermined rpm aboutrotary axis C and is in-fed in the Z direction to machine 1018 the workpiece. If desired, multiple passes are completed to cut a deeper thread.Lastly, the probe 22 is again loaded 1020 into the machine head 16 viathe automatic tool change arm 45 to inspect the finished thread anddiameters thereof by probing both the major and minor diameters of themachined work piece. If acceptable, the part is fed out of the machine.

Referring to FIGS. 1 and 11, each operation of the exemplary machiningcycle will be described in more detail using the pipe 12 a as anexemplary work piece 12. First, the pipe 12 a is loaded onto the worksupport 19. That is, the pipe 12 a is mounted onto the support arms 19 bof the table 19 and clamped thereon by the clamps 19 d. This loading ispreferably accomplished in the “off-line” or loading position L. Themachine table 19 with the pipe 12 a mounted/clamped thereon isautomatically shuttled to the operative position O via the movementdevice 28 when the machine center 10 is ready to machine the new part.

Next, the auto centering procedure will be completed. The tool magazine44 will rotate to position the touch sensor probe 22 stored thereonwithin the tool change position 46. The touch sensor probe 22 will beplaced into the machine head 16 from the tool magazine 44 by theautomatic tool change arm 45. The various components of the multi-axismachine head 18 will then move the probe 22 via the movement devices 35,37 and 39 to determine the actual pipe center 50 and the offset β fromthe projected center 58 as described above. The zero point 60 of themachine coordinate system 54 will be adjusted appropriately.

Once centered, the machining operation will begin. The multi-axismachine head 18 will first move the touch sensor probe 22 to theautomatic tool change position. The tool magazine 44 will then rotate toselect a desired threading tool 14 and exchange the touch sensor probe22 in the machine head 16 for the threading tool 14 in the tool magazine44 by using the automatic tool change arm 45. With the threading tool 14now in the machine head 16, the multi-axis machine head 18 will move tothe actual center 50 of the pipe 12 a and position the threading tool 14along the Z axis near the face of the pipe 12 a. The feed-out head 24will then move the threading tool 14 along the feed-out axis X1 to theproper diameter of the pipe 12 a for the first threading cut pass.

The machine head 16 will then rotate the rotary spindle 15 at theprogrammed RPM (i.e., generally between about 200 and about 500 rpm) andthe multi-axis head 18 will feed the threading tool 14 into the pipe 12in the Z direction to the programmed thread length at the programmedfeed rate. It will be appreciated by one skilled in the art that theprofile of the machined thread will generally depend on the depth of thecut, the feed rate of the machine tool, the rotation speed of the tool,and the number of passes. Once the cutting tool reaches the programmedlength along the machine Z axis, the tool 14 will be retracted along thefeed-out axis X1 from the part 12 a for clearance. The machine tool 18will then return the tool 14 along the Z axis to the start position.

Once back at the Z axis starting position, the threading tool 14 will bepositioned along the feed-out axis X1 at the proper diameter for asecond threading cut pass if so desired. This process will continue withthe tool 14 being positioned along the feed out axis X1 for eachthreading pass until the proper thread depth is reached. Once thethreading process is completed, the machine head 16 will stop rotatingthe rotary spindle 15 and the multi-axis machine head will position thethreading tool 14 in the automatic tool change position where it will beplaced back into the tool magazine 44 by the automatic tool change arm45.

The work support 19 with the threaded pipe 12 a mounted thereon will nowbe shuttled to an unload position U, where the pipe 12 a can bedismounted from the mounting device 20 “off-line” and the next loadedpart can immediately be shuttled to the operative machining position Owithin the machining center 10 for the process to continue. The new partis automatically centered and the process is repeated.

Turning to FIG. 13, an alternative work flow system 1050 is illustratedshowing a single-file material flow layout in which at least fourseparate machine centers 1052, 1054, 1056, and 1058 are position tomachine opposing ends of two work pieces 1060 and 1062 at the same time.That is, two work pieces are each in an operative position O1 and O2 atthe same time, which are preferably fed single file from a singleloading position L. In use, the work piece 12 is shuttled between themachine centers and loaded into one or the other of the operativepositions O1 or O2. Then, another work piece 12 to be machines isshuttled between the machine centers and loaded into the other of theoperative positions O1 or O2. When machining is complete on each workpiece, they are consecutively ejected from the machine, and new workpieces may then be again loaded by repeating the procedure.

It will be understood that various changes in the details, materials,and arrangements of the parts and components that have been describedand illustrated in order to explain the nature of the method andapparatus for machining work pieces may be made by those skilled in theart within the principle and scope of as described herein.

1. An apparatus for machining a curved surface on a pipe having alongitudinal center axis using a multi-axial machine head, the apparatuscomprising: a work support configured to hold the work piece stationarywithout rotary or translational movement of the work support or workpiece during the machining; a machine head configured to and operativeto move in a rotary direction and multiple linear directions relative tothe work piece including a machine head rotary direction, a machine headlinear feed-in direction along the longitudinal center axis, a machinehead linear feed-out direction orthogonal to the longitudinal centeraxis, and a machine head linear vertical direction orthogonal to thelongitudinal center axis, the rotary and multiple linear directions ofmovement of the machine head allowing for rapid mounting of the pipe tothe work support without the need for precision locators for aligningthe pipe on the work support; a rotary spindle positioned on the machinehead and configured to translate with the machine head relative to thepipe in the machine head linear feed-in direction, the machine headlinear feed-out direction, and the machine head linear verticaldirection and to rotate relative to the pipe about the longitudinalcenter axis for the curved surface with the feed-in direction beinggenerally parallel to the longitudinal center axis; and a thread cuttingtool mounted on the rotary spindle and configured to translate relativethereto in a tool feed-out direction relative to the machine head andorthogonal to the longitudinal center axis of the stationary curvedsurface to engage and to machine the stationary curved surface with themachine head linear feed-out direction used for large horizontaladjustments of the machine head and rotary spindle thereon and the toolfeed-out direction used for fine horizontal adjustments of the threadcutting tool for cutting threads to a precision depth.
 2. The apparatusof claim 1, having a plurality of work supports each supporting a pipeand each work support being positioned for shifting into: an operativeposition adjacent the machine head for machining; a loading position ofthe work support spaced from the operative position; and an unloadingposition where the work piece is removed from the work support.
 3. Theapparatus of claim 1, further comprising: a movement device operative toshuttle the respective work supports from the loading position to theoperative position.
 4. The apparatus of claim 2, further comprising: themachine head being located to face an open end of the stationary pipeduring the machining operation.
 5. The apparatus of claim 4, furthercomprising: a second machine head facing a second open end of the pipesuch that two ends of the pipe can be machined simultaneously, thesecond machine head configured to and operative to move in a rotarydirection and multiple linear directions relative to the pipe includinga second machine head rotary direction, a second machine head linearfeed-in direction along the longitudinal center axis, a second machinehead linear feed-out direction orthogonal to the longitudinal centeraxis, and a second machine head linear vertical direction orthogonal tothe longitudinal center axis; a second rotary spindle positioned on thesecond machine head and configured to translate with the second machinehead relative to the pipe in the second machine head linear feed-indirection, the second machine head linear feed-out direction, and thesecond machine head linear vertical direction and to rotate relative tothe pipe about the longitudinal center axis for the curved surface withthe second machine linear feed-in direction being generally parallel tothe longitudinal center axis and opposite to the machine hear linearfeed-in direction; and a second thread cutting tool mounted on thesecond rotary spindle and configured to translate relative thereto in asecond tool feed-out direction relative to the second machine head andorthogonal to the longitudinal center axis of the stationary curvedsurface to engage and to machine the second end of the pipe so that thesecond machine head linear feed-out direction is used for largehorizontal adjustments of the second machine head and second rotaryspindle thereon and the second tool feed-out direction is used for finehorizontal adjustments of the second thread cutting tool for cuttingthreads to a precision depth on the second end of the pipe.
 6. Theapparatus of claim 1, further comprising: a controller configured tocalculate the center axis of the pipe using inputs from a touch probeand configured to adjust a machine zero point of a machine coordinatesystem to the calculated center axis; and the spindle being mounted onthe apparatus which is configured to shift the spindle to align itsrotational axis to the pipe center axis.
 7. The apparatus of claim 1,further comprising: a thread cutting insert on the cutting tool to cut athread on an end of the pipe.